Field of the Invention
This invention relates to a method of manufacturing a stator of an electric rotating machine mounted to, for example, vehicles.
Description of the Related Art
An electric rotating machine that is mounted to a vehicle and used as a power generator or a motor, such as a magnet generator, has a multipolar stator. This multipolar stator has a stator core, which has radially-arranged teeth provided on the outer circumference of an annular yoke portion. Around the outer circumference of each of the teeth of this stator core, a stator coil is wound with an insulating material interposed therebetween. Because the stator coils of such a multipolar stator are affected by vibrations from the engine, a bonding process of bonding the coiled wires of the stator coils to each other with a resin such as a varnish is essential.
A conventionally known method of bonding the coiled wires of the stator coil of the electric rotating machine to be mounted in a vehicle is disclosed in, for example, JP-A-11-150923 (Patent Document 1), in which a varnish resin in liquid form is impregnated between the coiled wires and cured to bond the coiled wires to each other.
Another method of bonding the coiled wires is also known, as disclosed in JP-A-58-26552 (Patent Document 2). In this method, the coiled wires are bonded by bringing thermally meltable powder such as an epoxy resin into contact with the coiled wire surface of the stator coil that has been pre-heated so as to melt the thermally meltable powder, and then curing the thermally meltable powder.
Patent Document 1: JP-A-11-150923
Patent Document 2: JP-A-58-26552
However, conventional coil bonding methods have the following problems, because of circumstances such as an increase of engine vibration that is associated with higher vehicle output performance, a voltage increase in vehicle's power supply system, and maintenance of the coiled wire quality that is commensurate with these.
According to the method disclosed in Patent Document 1 above, it is possible to cause the varnish resin to permeate between the coiled wires and into the coiled wire lower layer portion because of its low viscosity. However, if the bonding of the coil end portion is insufficient and the engine vibration is large, it may be possible that the coil end portion can move and undergo fatigue failure.
In view of the problem, the coil end portion is conventionally bonded in the following manner. In order to bond the coil end portion sufficiently, the above-described bonding process with the varnish resin is performed, and thereafter, the coil end portion is bonded again with a high-viscosity liquid-type varnish resin.
According to the method disclosed in the foregoing Patent Document 2, bonding of the stator coil winding portion exterior, including the coil end portion, is sufficient, but insulation failure may occur between the coiled wires. The reason is as follows. The thermally meltable powder such as epoxy resin does not easily permeate between the coiled wires or into the coiled wire lower layer portion. For this reason, when the engine vibration is large, the coiled wires in the lower layer portion in particular move mutually, and because of the friction between the coiled wires, the insulating coating film on the coil surface wears out.
In addition, since the thermally meltable powder such as epoxy resin does not easily permeate between the coiled wires or into the coiled wire lower layer portion, an insulation failure may occur between the coils and between the coils and the stator core because of pin holes in the coil insulating coating film and pin holes in the core insulating film. The probability of this insulation failure between the coils and between the coils and the stator core becomes higher due to an increase in the voltage of the vehicle electric power supply system.
Furthermore, when merely both the bonding by the impregnation of the liquid-type varnish resin and the bonding by melting and curing the powdered resin are employed, there is a problem of extremely low productivity.